Comparing the influence of crestal cortical bone and sinus floor cortical bone in posterior maxilla bi-cortical dental implantation: a three-dimensional finite element analysis

Prognosis of Crestally Placed Short Plateau Implants in Posterior Maxilla

Crestal placement of short plateau implants in compromised jaws may cause implant failure due to bone overstress. The aim was to evaluate the impact of different sized implants on adjacent bone overload and the implant load-bearing ability in terms of the proposed index-ultimate functional load (UFL). Three-dimensional models of osseointegrated implants placed in types III and IV bone were analysed by the FEM for the case of patient-specific variations in cortical bone elasticity modulus. Maximum von Mises stresses in surrounding bone were calculated and compared with the cortical and cancellous bone ultimate strength characteristics to determine the UFL index for the studied implants. The implant UFL magnitudes were influenced by their dimensions, bone elasticity, and quality. The implant load-bearing ability was predetermined by cancellous bone strength. The maxilla with moderate elasticity modulus allows for the placement of wide short screwless implants in the compromised maxilla molar site with good clinical perspective.

Evaluation of reliability of zirconia materials to be used in implant-retained restoration on the atrophic bone of the posterior maxilla: A finite element study

PURPOSE

Zirconia materials have been used for implant-retained restorations, but the stress distribution of zirconia is not entirely clear. The aim of this study is to evaluate the stress distribution and risky areas caused by the different design of zirconia restorations on the atrophic bone of the posterior maxilla.

MATERIALS AND METHODS

An edentulous D4-type bone model was prepared from radiography of an atrophic posterior maxilla. Monolithic zirconia and zirconia-fused porcelain implant-retained restorations were designed as splinted or non-splinted. 300-N occlusal forces were applied obliquely. Stress analyses were performed using a 3D FEA program.

RESULTS

According to stress analysis, the bone between the 1) molar implant and the 2) premolar in the non-splinted monolithic zirconia restoration model was stated as the riskiest area. Similarly, the maximum von Mises stress value was detected on the bone of the non-splinted monolithic zirconia models.

CONCLUSION

Splinting of implant-retained restorations can be more critical for monolithic zirconia than zirconia fused to porcelain for the longevity of the bone.

Nonlinear Biomechanical Characteristics of the Schneiderian Membrane: Experimental Study and Numerical Modeling

Objective

The aim of this study is to quantify the nonlinear mechanical behavior of the Schneiderian membrane.

Methods

Thirty cadaveric maxillary sinus membrane specimens were divided into the elongation testing group and the perforation testing group. Mechanical experimental measurements were taken via ex vivo experiments. Theoretical curves were compared with experimental findings to assess the effectiveness of the nonlinear mechanical properties. The FE model with nonlinear mechanical properties was used to simulate the detachment of the Schneiderian membrane under loading.

Results

The mean thickness of the membrane samples was 1.005 mm. The mean tensile strength obtained by testing was 6.81 N/mm². In membrane perforation testing, the mean tensile strength and the linear elastic modulus were significantly higher than those in membrane elongation testing (P < 0.05). The mean adhesion force between the Schneiderian membrane and the bone was 0.052 N/mm. By FE modeling, the squared correlation coefficients of theoretical stress-strain curves for the nonlinear and linear models were 0.99065 and 0.94656 compared with the experimental data.

Conclusions

The biomechanical properties of the Schneiderian membrane were implemented into the FE model, which was applied to simulate the mechanical responses of the Schneiderian membrane in sinus floor elevation.

Primary implant stability in a bone model simulating clinical situations for the posterior maxilla: an in vitro study

PURPOSE

The aim of this study was to determine the influence of anatomical conditions on primary stability in the models simulating posterior maxilla.

METHODS

Polyurethane blocks were designed to simulate monocortical (M) and bicortical (B) conditions. Each condition had four subgroups measuring 3 mm (M3, B3), 5 mm (M5, B5), 8 mm (M8, B8), and 12 mm (M12, B12) in residual bone height (RBH). After implant placement, the implant stability quotient (ISQ), Periotest value (PTV), insertion torque (IT), and reverse torque (RT) were measured. Two-factor ANOVA (two cortical conditions×four RBHs) and additional analyses for simple main effects were performed.

RESULTS

A significant interaction between cortical condition and RBH was demonstrated for all methods measuring stability with two-factor ANOVA. In the analyses for simple main effects, ISQ and PTV were statistically higher in the bicortical groups than the corresponding monocortical groups, respectively. In the monocortical group, ISQ and PTV showed a statistically significant rise with increasing RBH. Measurements of IT and RT showed a similar tendency, measuring highest in the M3 group, followed by the M8, the M5, and the M12 groups. In the bicortical group, all variables showed a similar tendency, with different degrees of rise and decline. The B8 group showed the highest values, followed by the B12, the B5, and the B3 groups. The highest coefficient was demonstrated between ISQ and PTV.

CONCLUSIONS

Primary stability was enhanced by the presence of bicortex and increased RBH, which may be better demonstrated by ISQ and PTV than by IT and RT.

Sinus Floor Cortication: Classification and Prevalence

PURPOSE

To present a classification and assess the presence and degree of cortication of the sinus floor utilizing Computerized Tomography (CT) scan images.

MATERIALS AND METHODS

One hundred CT scans, of patient who required a sinus augmentation procedure (SAP), were evaluated and classified according to the Type of sinus floor cortication (SFC). Type 1: sinus floor showing similar or higher density than the surrounding cortical areas. Type 2: sinus floor showing less density than the surrounding cortical areas. Type 3: sinus floor showing no cortical bone. Type 4: sinus floor showing the fusion of sinus floor bone and native crestal bone.

RESULTS

The SFC were present in 31, 41, 18, and 10 cases in Type 1, 2, 3, and 4, respectively.

CONCLUSIONS

This classification based on the level of cortication of the sinus floor is clinically useful as a method of determining if the dental implant can be placed simultaneously or not with the SAP, or can be placed even without a SAP.